The uptake of glucose by rat hepatocytes, and the synthesis of glucose and glycogen will be studied. Glucose labelled with C14 and tritium will be used in conjunction with analytical techniques to distinguish between net uptake and recycling of glucose. The effects of diet and hormones, on glucose metabolism will be investigated. Hepatocyes from meal fed rats and acini prepared from mammary glands of lactating rats will be used to study fatty acid synthesis. Glucose and acids labelled with C14 and tritium will be used to determine the reactions that provide NADPH for reductive synthesis of fatty acids. The rate of the pentose cycle in liver cells will be measured and its role to supply reducing power for biosynthesis studied.